i'd bring back the the casino idea but make it like GTA.
then when Sazh leaves the casino, some First Person View style gunshooting.
from there a boss battle from standard third person view from LR 13. moves can be:
roll jump air fro (floats on way down) behind the back shot 2 hit kick combo (similar to sub zero's b4 from mkdc) which launches
gun pulled to side shot (2, triangle, whatever you call it)
hold aim (done by holding 2 or any other shot button input)
hands next to head shot - sazh will hold his hands near his head like he does at the end of cold blood... this is a good move to add to a string, like 22.
sweep, d3 (low poke), gunwhip (d1...similar to Kratos's d1 in mk9)
parry~cold blood, with just frames throughout it to extend it. NOT QTE and NOT SYNC. sync is a nice addition, but it isn't the highlight of the combo. the timing is. just frames > syncronized
behind the back parry - b2 can be behind the back shot, so parry version is b2~block... assuming LR 13 has real time blocking... WHICH IT BETTER
maybe some elbows.... make them after parrys...
square could be to shoot with left gun triangle could be to shoot with right gun some inputs could combine both, like behind the back shot x is jump circle - secondary weapon (synergy, fire2 etc) analog+block to roll block can be chosen by user (L2 or R2 or you can make L2 and R2 your block instead of just one button similar to mk trilogy on psx) parry b2+block, f1+block, etc